Summary: CHAPTER I
INTRODUCTION
High performance semiconductor devices with better voltage and current handling
capability are required in different fields like power electronics, computer and
automation. Since the invention of the germanium point contact transistor in 1948[1],
there has been all round progress in the science and technology of these devices. A
number of new devices have been developed and old technologies have been optimized
and modified by introducing better materials, designs and processes to meet the growing
need for better characteristics. Besides, higher voltage and current ratings, higher
switching frequency is also required for the compact design of Switch Mode Power
Supplies (SMPS), for high power efficiency in variable speed motors and for better
picture quality in TV deflection circuits. The power diode and transistor have been in use
in such applications for a long time. The technology of these devices is quite mature. To
meet the demand of still higher switching frequency, these devices are facing some
inherent constraints. While operating these devices in the ON state, there is storage of
minority charge carriers in various parts of the diode and transistor. These minority
charges cause storage time delay and affect the voltage and current conduction processes
during reverse recovery, (rr). The dissipation in the ON state and during reverse
recovery (rr), constrain the operation of the diode and BJTs to a switching frequency of
about 100 kHz. Large efforts have been made to decrease the losses in the ON state and